This section provides background information related to the present disclosure which is not necessarily prior art.
Shock absorbers are used in conjunction with automotive suspension systems and other suspension systems to absorb unwanted vibrations which occur during movement of the suspension system. In order to absorb these unwanted vibrations, automotive shock absorbers are generally connected between the sprung (body) and the unsprung (suspension/chassis) masses of the vehicle.
The most common type of shock absorbers for automobiles is the dashpot type which can be either a mono-tube design or a dual-tube design. In the mono-tube design, a piston is located within a pressure tube and is connected to the sprung mass of the vehicle through a piston rod. The pressure tube is connected to the unsprung mass of the vehicle. The piston divides the pressure tube into an upper working chamber and a lower working chamber. The piston includes compression valving which limits the flow of damping fluid from the lower working chamber during a compression stroke and rebound valving which limits the flow of damping fluid from the upper working chamber to the lower working chamber during a rebound or extension stroke. Because the compression valving and the rebound valving have the ability to limit the flow of damping fluid, the shock absorber is able to produce a damping force which counteracts the vibrations which would otherwise be transmitted from the unsprung mass to the sprung mass.
In a dual-tube shock absorber, a fluid reservoir is defined between the pressure tube and a reservoir tube which is positioned around the pressure tube. A base valve assembly is located between the lower working chamber and the fluid reservoir to control the flow of dampening fluid. The compression valving of the piston is moved to the base valve assembly and is replaced by a compression fluid valve assembly. In addition to the compression valving, the base valve assembly also includes a rebound fluid valve assembly. The compression valving of the base valve assembly produces damping force during a compression stroke, and the rebound valving of the piston produces damping force during a rebound or extension stroke. Both the compression and rebound fluid valve assemblies permit fluid flow in one direction, but prohibit fluid flow in an opposite direction; however, they are typically designed such that they do not generate a damping force but they may be designed to contribute to the generation of the damping force.
The valving for the shock absorber which determines the damping loads whether it is part of the piston assembly or the base valve assembly typically comprises one or more valve discs which is/are clamped or otherwise urged against an inner land or hub by some type of a retainer. When the inner portion of the valve disc is clamped or urged against the inner land or hub, the outer portion of the valve disc is biased against an outer land. The assembly of the valve discs against the lands defines flow restriction contours by means of the achieved interaction with the bending of the valve disc or the valve disc stack.
The pressure required to lift the valve discs off of the valve land is a key tuning feature for the shock absorber valve. With clamped discs that are clamped at their inner portion, this pressure control is typically done by adjusting the axial distance between the inner land or hub and the outer land of the piston or base valve. This difference in axial distance acts to apply a specified pre-stress to the valve discs allowing some pressure build up before the valve discs deflect and the valve opens. However, piston tooling is expensive and piston change-overs in production can be more time consuming than other valve components. This complicates the tuning of the shock absorber because any change in the axial distance between the inner land or hub and the outer land will require a new piston. The continued development of valve assemblies includes a new method of controlling the pre-stress applied to the valve discs which is lower in cost and easier to accommodate changes in the amount of pre-stress.